The BHU Future Farming Centre

Information - The FFC Bulletin - 2014 V2 March

Subscription information Disclaimer, copyright and licensing

Fire-resistant shelter belts

By Molly Shaw

Last September many shelter belts in Canterbury were blown down or damaged, and land owners now have an opportunity to re-assess the reasons for having shelter in their fields. Sure, there has been a trend toward cutting down shelters in irrigated pastures the past few years. But as climate change research predicts that Canterbury will be a hotter, drier place in the next few decades, the economic picture may not always look like it does now.

Farmers expect shelter belts to benefit them in some or all of the following ways:

  • Wind breaks to reduce drought stress on pasture (even farmers with access to irrigation can’t run it for free)
  • Shelters for livestock during southerlies
  • Habitat for beneficial species that subsequently decrease pest pressure in crops
  • Some degree of nutrient scavenging to reduce leaching into water sources, particularly for shelter belts lining streams or ditches

For the ecologically minded, you can add the less tangible benefits of preserving native species, aesthetic appeal, etc. Landowners prioritize one or more of the above benefits, take into account establishment cost and plant growth rate, and then choose shelterbelt species accordingly. In the past, species like pines, macrocarpa, gorse and poplar have come out on top.

Now we have one more characteristic to take into consideration: flammability. The tendency for vegetation to facilitate fire spread will become more and more important in Canterbury’s hotter, drier future.

Wild fires are most likely to break out and spread at a devastating rate when we’ve had a hot, dry summer. It’s easy to think back to this past summer, cool and wet as it was, and wonder what we’re worrying about. But think back one more year to the heat and drought of the 2012-2013 summer—that’s the type of summer predicted to become more common in the upcoming few decades.

Flammability isn’t rocket science. Remember your basic scout fire building skills? Fires catch best in super dry, lightly packed, twiggy material, and these qualities vary between plant species. Fire spreads quickest in plants that:

  1. Hold more dead material (dead plant matter is drier than live and requires less energy to ignite)
  2. Hold fuel, especially small twigs, evenly spaced along the branches, facilitating fire spread
  3. Contain oils and resins—sparks flying ahead of the fire can ignite these substances easily

For example, young gorse isn’t rated as highly flammable but older plants are highly flammable because they can be made up of 65% dead material arranged neatly along the branches. And manuka and kanuka burn with high intensity probably due to the essential oils they contain and their small leaves which are continuously spaced along their branches.

In wet conditions or if you irrigate your shelter belts, then species choice probably isn’t so important when it comes to flammability—regardless of what it is, if it’s wet then it generally won’t burn. But if you don’t have irrigation, or it doesn’t reach to the shelter belts, then read on.

In 2001, the NZ Fire Service Commission harnessed the experience of about 60 fire managers via surveys, asking them about their experience with fires in different native NZ species. The information gathered is somewhat subjective, but trends did emerge, see figure 1.

Figure 1: Flammability guide for 42 NZ native trees and shrubs [1].

Botanical Name

Maori/European Name

Flammability class

Kunzea ericoides

kanuka

High

Leptospermum

scoparium manuka

High

Cyathea and Dicksonia spp.

tree ferns

Moderate/High

Cyathodes fasciculata

mingimingi

Moderate/High

Dodonea viscosa

ake ake

Moderate/High

Phormium cookianum and P. tenax

flax/harakeke

Moderate/High

Podocarpus totara

totara

Moderate/High

Agathis australis

kauri

Moderate

Beilschmiedia

tawa tawa

Moderate

Dacrydium cupressinum

rimu

Moderate

Metrosideros umbellata

southern rata

Moderate

Pittosporum tenuifolium

kohuhu

Moderate

Podocarpus dacrydioides

kahikatea/white pine

Moderate

Weinmannia silvicola

tawhero/towhai

Moderate

Aristotelia serrata

makomako/wineberry

Low/Moderate

Cordyline australis

ti kouka/cabbage tree

Low/Moderate

Coriaria arborea

tutu

Low/Moderate

Hebe salicifolia and H. stricta

koromiko

Low/Moderate

Hoheria spp.

houhere/hoheria/lacebark

Low/Moderate

Knightia excelsa

rewarewa

Low/Moderate

Melicytus lanceolatus

mahoe wao

Low/Moderate

Melicytus ramiflorus

mahoe/whiteywood

Low/Moderate

Myoporum laetum

ngaio

Low/Moderate

Nothofagus menziesii

tawhai/silver beech

Low/Moderate

Phyllocladus glaucus

toatoa

Low/Moderate

Pittosporum crassifolium

karo

Low/Moderate

Pittosporum eugenioides

tarata/lemonwood

Low/Moderate

Plagianthus regius

manatu/ribbonwood

Low/Moderate

Weinmannia racemosa

kamahi

Low/Moderate

Carpodetus serratus

putaputaweta

Low

Coprosma grandifolia

raurekau, kanono

Low

Coprosma repens

taupata

Low

Coprosma robusta

karamu

Low

Corynocarpus laevigatus

karaka

Low

Fuchsia excorticata

kotukutuku/fuchsia

Low

Geniostoma ligustrifolium

hangehange

Low

Griselinia littoralis

papauma/broadleaf

Low

Griselinia lucida

puka

Low

Macropiper excelsum

kawakawa/pepper tree

Low

Psuedopanax arboreum

five finger

Low

Pseudopanax crassifolius

horoeke/lancewood

Low

Solanum aviculare

poroporo

Low

Tim Curran, ecologist and lecturer at Lincoln University, has been researching flammability of plants grown in NZ and was able to add comments about non-natives used for shelter belt species. He classifies some of the most common shelter belt species as highly flammable, such as:

  • Eucalyptus, e.g. manna gum E. viminalis (high in natural oils)
  • Pines, such as radiata pine, especially when it retains dead material
  • gorse (especially old gorse hedges with high levels of dead material)

Deciduous species such as willow and poplar tend to have leaves with higher moisture content and therefore are quite a bit less flammable.

Dr. Curran’s recommended low-flammability species for shelter belts are:

  • Broadleaf (Griselinia spp.)
  • Coprosma species
  • Pseudopanex (five-finger, lancewood)
  • Pittosporum eugenioides (lemonwood)

Admittedly, these species are slower growing than the standard pines and macrocarpa often used for shelter belts. A compromise might be to plant the slow-growing natives interspersed with fast-growing non-natives, then remove the big trees as the native ones mature. It is important to realize that if the weather is hot and dry enough, even the low flammability species are likely to burn.

Dr Curran’s Plant combustion BBQ measuring maximum burning temperature

Dr. Curran’s research team is currently conducting flammability tests of NZ shelterbelt species in order to make objective recommendations for “green fire break” plantings, lines of low-flammability species that could serve as fire breaks in the greater Canterbury landscape.

References and further reading

Fogarty, L.G., A flammability guide for some common New Zealand native tree and shrub species, New Zealand Fire Service Commission Research Report. 2001. http://www.fire.org.nz/Research/Published-Reports/Documents/89fa12a030b48531cf396dcdba52c6e2.pdf

Berry, Z.C., Wevill, K., and Curran, T.J., The invasive weed Lantana camara increases fire risk in dry rainforest by altering fuel beds. Weed Research, 2011. 51(5): p. 525-533. http://dx.doi.org/10.1111/j.1365-3180.2011.00869.x.  Please email This email address is being protected from spambots. You need JavaScript enabled to view it. if you would like an ePrint of this paper

Lantana fuels rainforest fires ABC Science (web page)

Shelter and nature conservation in Canterbury – a practical guide ECan (PDF file)

Botanical Name

Maori/European Name

Flammability class

Kunzea ericoides

kanuka

High

Leptospermum

scoparium manuka

High

Cyathea and Dicksonia spp.

tree ferns

Moderate/High

Cyathodes fasciculata

mingimingi

Moderate/High

Dodonea viscosa

ake ake

Moderate/High

Phormium cookianum and P. tenax

flax/harakeke

Moderate/High

Podocarpus totara

totara

Moderate/High

Agathis australis

kauri

Moderate

Beilschmiedia

tawa tawa

Moderate

Dacrydium cupressinum

rimu

Moderate

Metrosideros umbellata

southern rata

Moderate

Pittosporum tenuifolium

kohuhu

Moderate

Podocarpus dacrydioides

kahikatea/white pine

Moderate

Weinmannia silvicola

tawhero/towhai

Moderate

Aristotelia serrata

makomako/wineberry

Low/Moderate

Cordyline australis

ti kouka/cabbage tree

Low/Moderate

Coriaria arborea

tutu

Low/Moderate

Hebe salicifolia and H. stricta

koromiko

Low/Moderate

Hoheria spp.

houhere/hoheria/lacebark

Low/Moderate

Knightia excelsa

rewarewa

Low/Moderate

Melicytus lanceolatus

mahoe wao

Low/Moderate

Melicytus ramiflorus

mahoe/whiteywood

Low/Moderate

Myoporum laetum

ngaio

Low/Moderate

Nothofagus menziesii

tawhai/silver beech

Low/Moderate

Phyllocladus glaucus

toatoa

Low/Moderate

Pittosporum crassifolium

karo

Low/Moderate

Pittosporum eugenioides

tarata/lemonwood

Low/Moderate

Plagianthus regius

manatu/ribbonwood

Low/Moderate

Weinmannia racemosa

kamahi

Low/Moderate

Carpodetus serratus

putaputaweta

Low

Coprosma grandifolia

raurekau, kanono

Low

Coprosma repens

taupata

Low

Coprosma robusta

karamu

Low

Corynocarpus laevigatus

karaka

Low

Fuchsia excorticata

kotukutuku/fuchsia

Low

Geniostoma ligustrifolium

hangehange

Low

Griselinia littoralis

papauma/broadleaf

Low

Griselinia lucida

puka

Low

Macropiper excelsum

kawakawa/pepper tree

Low

Psuedopanax arboreum

five finger

Low

Pseudopanax crassifolius

horoeke/lancewood

Low

Solanum aviculare

poroporo

Low

Normal 0 false false false MicrosoftInternetExplorer4